This application is based on Japanese Patent Application No. 2000-221643, filed in Japan on Jul. 24, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
This invention relates to a fuel injection valve for an internal combustion engine.
2. Description of the Related Art
Fuel injection valves are widely used to supply fuel to internal combustion engines. One example of a known fuel injection valve for use with an internal combustion engine is disclosed in Japanese Published Unexamined Patent Application Hei 9-14090. FIG. 6 is a cross-sectional elevation of a fuel injection valve disclosed in that publication, and FIG. 7 is an enlarged view of the lower end of the fuel injection valve of FIG. 6.
The illustrated fuel injection valve 1 includes an electromagnetic coil 3, a stationary ferromagnetic core 4, and metal plates 5 defining a magnetic path, all disposed in a resin housing 2. The electromagnetic coil assembly 3 includes a resin bobbin 3a, a coil 3b which is wound around the outer periphery of the bobbin 3a, and a terminal 6 which is electrically connected to the coil 3b and which enables the coil 3b to be electrically connected to an external source of electric power. The resin housing 2 is molded around the electromagnetic coil assembly 3.
An adjuster 8 for adjusting the load of a compression spring 7 is secured inside the stationary core 4. Two metal plates 5 (only one of which is visible) which form a magnetic path each have one welded to the stationary core 4 and another end welded to a magnetic pipe 9 which forms a magnetic path. A non-magnetic pipe 11 is disposed between and secured to the fixed core 4 and the magnetic pipe 9 such that a movable ferromagnetic core 10 disposed inside the magnetic pipe 9 can move up and down.
One end of the movable core 10 is welded to a needle 101, and the other end of the movable core 10 abuts against the compression spring 7. A valve head 101a is formed on the other end of the needle 101 and is guided with respect to a valve seat 102 by a guide portion 101b. 
The valve head 101a is moved between an open and a closed position by an electromagnetic drive mechanism disposed at the upper portion. The valve head 101a opens and closes the valve by moving out of or into contact with the top surface of the valve seat 102. When the valve head 101a is in an open position, fuel flows past the valve head 101a to an orifice plate having discharge orifices 103 formed therein and is sprayed from the discharge orifices 103 to the exterior of the fuel injection valve into an internal combustion engine.
In the conventional fuel injection valve shown in FIGS. 6 and 7, the direction of fuel injection is determined by the angle of inclination of the discharge orifices 103 in the orifice plate with respect to the longitudinal axis of the fuel injection valve 1. Upstream of the orifice plate, fuel flows from the outer peripheral portion to the inner peripheral portion, so it is difficult to obtain a large spray angle for the fuel. Furthermore, when manufacturing a one-spray type having a large spray angle (such as approximately 15 degrees or greater) or a two-spray type having a large spray angle (such as approximately 15 degrees or greater), it is necessary to make the angle of inclination of the discharge orifices 103 large, so it is difficult to form the discharge orifices so as to have a small diameter, and it is difficult and to make the diameter of the discharge orifices 103 small to obtain atomization of the fuel. Even if discharge orifices 103 with a large angle of inclination and a small diameter can be formed, the manufacturing costs for forming such discharge orifices are significant. This is especially the case with respect to an orifice plate having at least six discharge orifices 103 to promote atomization, since with such an orifice plate the diameter of the discharge orifices 103 becomes particularly small, so processing of the orifice plate becomes very difficult.
By increasing the ratio L/xcfx86d of the length L of the discharge orifices 103 to their diameter xcfx86d, the spray direction can be regulated and the spray angle can be increased, but in this case, the atomization of the fuel is worsened. Furthermore, when L/xcfx86d is made large, it becomes difficult to form the discharge orifices 103 in the orifice plate, and increasing the angle of inclination of the discharge orifices 103 increases the difficulty of forming the discharge orifices in the orifice plate, resulting in extreme increases in manufacturing costs.
Japanese Published Unexamined Patent Application Hei 10-122096 discloses a fuel injection valve having a dish-shaped orifice plate in which a fuel cavity is formed. Such an orifice plate is extremely expensive to manufacture.
The present invention provides a fuel injection valve which can have discharge orifices with a small diameter to promote atomization of fuel without an orifice plate containing the discharge orifices being expensive to manufacture.
According to one form of the present invention, a fuel injection valve includes an orifice plate having a plurality of discharge orifices formed therein. A valve seat is disposed upstream of the discharge orifices and has a cylindrical fuel passage formed therein. A fuel cavity is formed between the cylindrical fuel passage and the orifice plate directly above the discharge orifices. A valve member is supported for reciprocating movement into and out of contact with the valve seat. The fuel injection valve satisfies the inequalities
xcfx86D1+xcfx86d less than xcfx86P and t less than xcfx86d 
wherein xcfx86D1 is the diameter of the cylindrical fuel passage, xcfx86d is the diameter of each discharge orifice, xcfx86P is the diameter of an imaginary circle passing through the center of each discharge orifice, and t is the depth in the axial direction of the fuel cavity.
In a preferred embodiment, the fuel injection valve satisfies the inequality
1 less than S2/S1 less than 3 
wherein S1 is the total cross-sectional area of the discharge orifices, and S2 is the surface area of a cylindrical surface having a diameter equal to the diameter xcfx86D1 of the cylindrical fuel passage and a height equal to the axial depth t of the fuel cavity.
In a preferred embodiment, the fuel cavity is formed in the valve seat, and the orifice plate is a flat member.